1. Field of the Invention
The present invention relates to a liquid crystal display device that is manufactured by using the COG method in which driver ICs are mounted on the peripheral portion of one of two insulative substrates that are opposed to each other with a liquid crystal layer interposed in between, as well as to a testing method of such a liquid crystal display device.
2. Description of the Related Art
With the progress of the highly information-oriented society, great advances are being made in the field of liquid crystal display devices. To spread liquid crystal display devices further, it is now important to decrease their prices by improving their productivity.
In conventional liquid crystal display devices, a driver LSI for driving the switching elements of pixels is provided in the form of a TCP (tape carrier package) and is connected, via an ACF (anisotropic conductive film), to electrode terminals formed on the surface of the peripheral portion of one of two insulative substrates that are opposed to each other with a liquid crystal layer interposed in between. The TCP is such that a driver LSI having Au bumps is mounted on a flexible circuit board by connecting the former to the latter with an Au/Sn eutectic alloy. The flexible circuit board is a circuit board that is formed by sticking copper foil to a polyimide film, forming a circuit by photolithography, and then plating the circuit with Sn. The ACF is a film that is configured in such a manner that plastic particles plated with Ni/Au, Ni particles, or the like are dispersed in an insulative resin such as an epoxy resin. With this method, if a display failure such as a line defect is found in a dynamic operating inspection that is performed after the TCP has been connected to the peripheral portion of the substrate, it can easily be judged whether the cause of the display failure exists in the driver LSI or a wiring or switching elements formed on the circuit board by bringing a prober that is connected to an oscilloscope to copper-foil-exposed tip portions of an output terminal array of the TCP and measuring output waveforms of the driver LSI. Further, the cause of a failure of the driver LSI can be determined by analyzing the measured waveforms of the driver LSI, which makes it possible to increase the yield of driver LSI products and thereby provide inexpensive liquid crystal display devices.
On the other hand, in recent years, the COG (chip on glass) method has come to be employed increasingly as a lower-cost manufacturing method of a liquid crystal display device. A method of connecting a driver LSI and external circuits to an electrode terminal portion of a general liquid crystal display device by using the COG method will be described below with reference to FIG. 9. First, an ACF 10 is stuck to electrode terminals 17 that are formed on the surface of the peripheral portion of an electrode substrate 1. After Au bump electrodes 3a and 3b that are formed on the back face of a driver LSI 3 are brought into accurate alignment with the electrode terminals 17, thermo-compression bonding is performed by using a heating/pressurizing tool under conditions that the heating temperature is 170-200xc2x0 C., the bonding time is 10-20 seconds, and the pressure is 30-100 Pa. As a result, vertical continuity is established by conductive particles 10a of the ACF 10 that are interposed between the bump electrodes 3a and 3b of the driver LSI 3 and the electrode terminals 17. Horizontal insulation is maintained because an insulative epoxy resin 10b exists around the conductive particles 10a. In this manner, the driver LSI 3 is directly mounted on the electrode terminals 17. Further, to transmit drive signals and power from the external circuit board to the driver LSI 3, an FPC (flexible printed circuit) 9 is connected to the electrode terminals 17 in a similar manner.
Where the above-described COG method is employed, the bump electrodes 3a and 3b of the driver LSI 3 exist on the back face of the driver LSI 3 and are surrounded by the ACF 10. If a display failure such as a line defect occurs in a dynamic operating inspection that is performed in this state, that is, after the mounting of the driver LSI 3, output waveforms of the driver LSI 3 cannot be measured. Therefore, it cannot be determined whether the cause of the display failure exists in the driver LSI 3 or a wiring or switching elements formed on the electrode substrate 1. This makes it impossible to take an effective measure against the failure and hence makes it difficult to increase the yield.
To solve the above problem, JP-A-9-26591, for example, proposes a liquid crystal display device in which electrodes for connection to a driver LSI and test pads for contact with a prober are separately provided on an output wiring that is formed on a substrate surface. However, in this case, it is difficult to secure an area where to form test pads when the number of output terminals of a driver LSI is large. Securing such an area is a factor of obstructing the narrowing of the frame portion of a liquid crystal display device.
Another method for solving the above problem is known. In connecting a driver LSI to electrode terminals using an ACF, thermo-compression bonding is performed for such a short time that the resin in the ACF reacts only slightly. A dynamic operating inspection is performed thereafter. Thermo-compression bonding is performed again for a sufficient time only if a test result is good. If a display failure is found, the driver LSI is removed immediately and replaced by another one. However, this method is disadvantageous in making the process complex and lowering the productivity.
The present invention has been made to solve the above problem, and an object of the invention is therefore to provide, in a liquid crystal display device that employs the COG method, a structure that makes it possible to easily determine the cause of a display failure such as a line defect as well as a related testing method, thereby obtaining a liquid crystal display device that is inexpensive and high in productivity.
A liquid crystal display device according to a first aspect of the invention comprises a display unit, a driving line array, a driver IC and at least one cross line. The display unit includes two insulative substrates opposed to each other and a liquid crystal layer interposed between the two insulative substrates for forming liquid crystal display elements. The driving line array is formed on a peripheral portion of one of the two insulative substrates and including driving lines that are connected to the respective liquid crystal display elements. The driver IC is mounted on the peripheral portion, for driving the liquid crystal display elements, the driver IC having input bumps for receiving input signals from an external circuit board and output bumps that are joined to the respective driving lines. And the one cross line is formed on the peripheral portion so as to cross the driving line array with an insulating film interposed in between, the cross line has an electrode with which a prober can come into contact.
According to the first aspect of the invention, if a display failure such as a line defect is found in a dynamic operating inspection that is performed after mounting of the driver IC, a crossing portion of the cross line and a driving line as a failure occurring position is irradiated with laser light, whereby the driving line concerned and the cross line are connected to each other. An output waveform of the driver IC flowing through the driving line concerned can be measured via the cross line by contacting a prober into contact with the electrode. In this manner, the cause of a display failure can be investigated easily, which makes it possible to provide a liquid crystal display device that is inexpensive and high in productivity.
A liquid crystal display device according to a second aspect of the invention comprises a display unit, at least two cascade-connected ICs, a connection line array and at least one cross line. The display unit includes two insulative substrates opposed to each other and a liquid crystal layer interposed between the two insulative substrates for forming liquid crystal display elements. The two cascade-connected driver ICs include first and second driver ICs mounted on a peripheral portion of one of the two insulative substrates, for driving the liquid crystal display elements. The first driver IC has an output bump array for outputting output signals that are supplied to the respective liquid crystal display elements. The second driver IC has an input bump array for receiving the output signals from the first driver IC. The connection line array is formed on the peripheral portion and includes connection lines that connect the output bump array of the first driver IC to the input bump array of the second driver IC. The one cross line is formed on the peripheral portion so as to cross the connection line array with an insulating film interposed in between, the cross line having an electrode with which a prober can come into contact.
According to the second aspect of the invention, if a display failure such as a line defect is found in a dynamic operating inspection that is performed after mounting of the driver ICs, a crossing portion of the cross line and a connection line as a failure occurring position is irradiated with laser light, whereby the connection line concerned and the cross line are connected to each other. An output waveform of the first driver IC flowing through the connection line concerned can be measured via the cross line by contacting a prober into contact with the electrode. In this manner, the cause of a display failure can be investigated easily, which makes it possible to provide a liquid crystal display device that is inexpensive and high in productivity.
A third aspect of the invention provides a testing method for determining a cause of a display failure such as a line defect when it has occurred in a manufacturing process of a liquid crystal display device. The liquid crystal display device comprises a display unit, a driving line array, a driver IC and at least one cross line. The display unit includes two insulative substrates opposed to each other and a liquid crystal layer interposed between the two insulative substrates for forming liquid crystal display elements. The driving line array is formed on a peripheral portion of one of the two insulative substrates and includes driving lines that are connected to the respective liquid crystal display elements. The driver IC is mounted on the peripheral portion, for driving the liquid crystal display elements, the driver IC has output bumps that are joined to the respective output lines. The one cross line is formed on the peripheral portion so as to cross the output line array with an insulating film interposed in between, the cross line has an electrode with which a prober can come into contact. The testing method comprises the steps of determining an address of a position where the display failure has occurred; irradiating a crossing portion of the cross line and the driving line corresponding to the determined address with laser light, and thereby connecting the cross line and the driving line for that crossing portion; and contacting a prober that is connected to an oscilloscope into contact with the electrode of the cross line and thereby measuring an output waveform of the driver IC flowing through the driving line via the cross line and the electrode.
According to the third aspect of the invention, a test process is executed that includes the steps of determining an address of a position where a display failure has occurred; irradiating a crossing portion of the cross line and the driving line corresponding to the determined address with laser light, and thereby connecting the cross line and the driving line for that crossing point; and contacting a prober that is connected to an oscilloscope into contact with the electrode of the cross line and thereby measuring an output waveform of the driver IC flowing through the driver line via the cross line and the electrode. Therefore, when a display failure such as a line defect has occurred in a manufacturing process of a liquid crystal display device having driving lines and a cross line, the cause of the display failure can be determined.
A fourth aspect of the invention provides a testing method for determining a cause of a display failure such as a line defect when it has occurred in a manufacturing process of a liquid crystal display device. The liquid crystal display device comprises a display unit, at least two cascade-connected driver ICs, a connection line array and at least one crossing line. The display unit includes two insulative substrates opposed to each other and a liquid crystal layer interposed between the two insulative substrates for forming liquid crystal display elements. The two cascade-connected driver ICs include first and second driver ICs. The two cascade-connected driver ICs are mounted on a peripheral portion of one of the two insulative substrates, for driving the liquid crystal display elements. The first driver IC has an output bump array for outputting output signals that are supplied to the respective liquid crystal display elements. The second driver IC has an input bump array for receiving the output signals from the first driver IC. The connection line array is formed on the peripheral portion and includes connection lines that connect the output bump array of the first driver IC to the input bump array of the second driver IC. The one cross line is formed on the peripheral portion so as to cross the connection line array with an insulating film interposed in between, the cross line has an electrode with which a prober can come into contact. The testing method comprises the steps of determining one connection line in the connection line array connected to one liquid crystal display element that the display failure has occurred; irradiating one crossing portion of the cross line and the one connection line with laser light, and thereby connecting the cross line and the connection line for the one crossing portion; and contacting a prober that is connected to an oscilloscope into contact with the electrode of the cross line and thereby measuring an output waveform of the driver IC flowing through the connection line via the cross line and the electrode.
According to the fourth aspect of the invention, a test process is executed that includes the steps of determining one connection line in the connection line array connected to one liquid crystal display element that the display failure has occurred; irradiating one crossing portion of the cross line and the one connection line with laser light, and thereby connecting the cross line and the connection line for the one crossing portion; and contacting a prober that is connected to an oscilloscope into contact with the electrode of the cross line and thereby measuring an output waveform of the driver IC flowing through the one connection line via the cross line and the electrode. Therefore, when a display failure such as a line defect has occurred in a manufacturing process of a liquid crystal display device of such a type as to have connection lines that connect the output bumps of a first driver IC and the input bumps of a second driver IC, the cause of the display failure can be determined.